1. Field of the Invention
This invention relates to gyroscopes for detecting the rotational angular velocity of an object, and in particular to vibratory gyroscopes which determine the rotational angular velocity by determining the Coriolis force acting on the object.
2. Description of the Related Art
Gyroscopes are used for detecting rotational angular velocity in car navigation systems, inertial navigation systems and attitude control systems for aircrafts and ships, attitude control systems for robots and unmanned vehicles and apparatuses for producing a stable image in TV cameras and video cameras.
The gyroscopes used in the foregoing various industrial applications must be small in size. Therefore, vibratory gyroscopes, which are typically smaller than other types of gyroscopes, have attracted attention.
FIG. 32 shows a conventional vibratory gyroscope. The vibratory gyroscope comprises a columnar vibrator 1 made of isoelastic metal (Elinvar) to which a drive piezoelectric device 2 and a detection piezoelectric device 3 are secured. When the vibrator 1 is rotated about a Z-axis while the drive piezoelectric device 2 supplies, to the vibrator 1, bending vibrations in the direction of an X-axis, Coriolis force acts on the vibrator 1 such that the vibrator 1 is vibrationally deformed in the Y-axis direction. The amount of deformation in the Y-axis direction is detected by the piezoelectric device 3 as a voltage signal.
Assuming that the mass of the vibrator 1 is m, the velocity of the applied vibrations in the X-axis direction is v (a vector value) and the angular velocity about the Z-axis is .omega., the Coriolis force F (a vector value) is as follows: EQU F=2m(v.times..omega.)
where symbol x indicates a vector cross product.
As described above, the Coriolis force F is proportional to the angular velocity .omega.. Therefore, if the deforming vibrations of the vibrator 1 in the Y-axis direction are converted into a voltage signal by the detection piezoelectric device 3, the angular velocity .omega. can be obtained by measuring the voltage signal.
However, because the vibratory gyroscope shown in FIG. 32 has a structure in which the vibrator 1 is driven to vibrate in the X-axis direction and is deformed in the Y-axis direction by the Coriolis force, only an angular velocity .omega. about the Z-axis (that is, the longitudinal or major axis of the vibrator 1) can be detected. Therefore, the vibratory gyroscope can only be mounted on a surface of a rotating object which is perpendicular to the Z-axis. This restricts the use of the vibratory gyroscope in a variety of apparatuses in which such a surface is not readily available.
Moreover, if it is desired to detect rotational angular velocity in two- or three-dimensional directions using the vibratory gyroscope of the foregoing type, two or more vibrators 1 of the type shown in FIG. 32 must be arranged such that the major axes of the respective vibrators 1 are perpendicular to each other. Further, when it is desired to detect rotational angular velocity in three-dimensional directions, two of the vibratory gyroscopes may be arranged in the plane of a substrate, but it is necessary to arrange the third vibratory gyroscope such that it projects perpendicular to the substrate. In this arrangement, a space required for the three vibratory gyroscopes is substantially increased to accommodate the third vibratory gyroscope.
Furthermore, the vibratory gyroscope shown in FIG. 32 is only able to detect bending vibrations due to the Coriolis force--that is, the vibratory gyroscope cannot detect torsional vibrations. Since the vibration mode is limited only to bending vibrations, the applications of the conventional vibratory gyroscope is narrowed undesirably.
In addition, the above-mentioned conventional vibratory gyroscope is only able to detect the angular velocity of a rotating system about one axis. In order to detect the angular velocity of rotating system about two axes, two conventional vibrators must be employed. In order to detect angular velocity of a rotating system about three axes, three conventional vibrators must be employed.